With the increasing drilling scale of oil and gas fields and the development of science and technology, especially the rapid development of a LWD technology, it is urgent to make the present advanced science and technology play an important role in the development of the oil and gas fields. An azimuthally acoustic LWD technology is one of LWD technologies. Acoustic LWD realizes acoustic logging while drilling. Compared with wireline logging, the acoustic LWD obtains data which is less affected by invasion of a drilling fluid and can relatively effectively detect the lithological characters and physical properties and reservoir parameter of a borehole wall stratum. Compressional wave and shear wave velocities of the stratum are obtained by an acoustic LWD instrument. A pore pressure gradient and a permeability are established, a borehole stability is assessed, a lithological character change is explained, and a flow effect of fluid in a borehole is detected, thus important geological guidance information is provided for a drilling operation. However, since the acoustic LWD is affected by noise of a drilling tool, circulation of the drilling fluid and drill collar waves, in order to obtain high-quality data, technologies such as drill collar sound insulation, high-precision measurement, high-power acoustic transmission and high-sensitivity acoustic reception are essential. However, developing a transmitting apparatus and a receiving apparatus of the transducer has become a bottleneck problem due to problems involved in the installation, water tightness, pressure imbalance, as well as conflicts between low frequency and light weight and small size of the acoustic wave transducer in practical applications.
The azimuthally acoustic while drilling signal receiving transducer encapsulating structure mainly employs two structural solutions:
(1) an acoustic while drilling receiving apparatus based on a button-shaped receiving transducer may be suitable for monopole, dipole and multi-pole acoustic while drilling instruments. Since the button-shaped receiving transducer used is higher in receiving sensitivity, an acoustic signal transmitted by the acoustic transmitting apparatus can be well received in the LWD and due to a special structure of such a button-shaped receiving transducer, the transducer is easily damaged during operation; and
(2) an acoustic while drilling receiving apparatus employing an annularly-potted receiving transducer is mainly used in a monopole acoustic while drilling instrument since multiple transducers are encapsulated in the same annular ribbon and are mutually connected in parallel.
However, the acoustic while drilling receiving apparatus based on a button-shaped receiving transducer is prone to failure since the button-shaped receiving transducer is easily damaged. Since the transducers realize high-pressure sealing with the drill collar while being installed on a frame of an internal electronic bin, such a structure increases requirements for machining and assembling the frame of the internal electronic bin and the external drill collar. Further, the receiving apparatus requires to be specially serially connected with a devices for borehole diameter measurement so that extremely high requirements for connection and reliability of the instrument are presented. However, the acoustic while drilling receiving apparatus based on an annularly-potted receiving transducer is mainly used in the monopole acoustic while drilling instrument.
In terms of the borehole diameter measurement, a hydraulic balance apparatus is required for encapsulation when a traditional ultrasonic distance detecting sensor is encapsulated; and however, it is larger in volume after hydraulic encapsulation is completed, and generally, may be directly mounted in the electronic bin or internal frame, accordingly, a space of a water hole inside the drill collar is occupied, resulting in complex structure and reduced reliability.